The present application claims priority from Japanese Patent Application Serial No.2002-240044 filed on Aug. 21, 2002. Applicant claims priority under 35 U.S.C. xc2xa7119 as to said Japanese application, and the entire disclosure of that application is incorporated herein by reference.
The present invention relates to an arm lowering motion restricting device for a working vehicle. More particularly, the present invention relates to an arm lowering motion restricting device for a working vehicle which has arms that are pivotably connected to a mobile vehicle so that these arms can be freely raised and lowered, a working tool that is detachably attached to the tip end portions of these arms, and raising and lowering cylinders that cause the raising and lowering motion of these arms.
Generally, working vehicles in which a bucket that can be freely swung upward and downward is attached to the tip end portion of an arm that can be freely raised and lowered are used in order to dig in the ground, move earth that has been dug from the ground and the like. For example, such working vehicles comprise an operating cabin which is disposed on the central upper portion of a mobile moving body, a pair of arms which extend in the forward-rearward direction on both the left and right sides of the operating cabin, and which are pivotably connected so that these arms can be freely raised and lowered, a bucket which is detachably attached to the tip end portions of these arms, and raising and lowering cylinders which cause the raising and lowering motion of these arms. A reinforcing member which straddles the space between the arms is attached to the tip end portions of the arms, the cylinder rod end portions of the raising and lowering cylinders are pivotably connected to the tip end portions of the arms, and the cylinder tube end portions of the raising and lowering cylinders are pivotably connected to the moving body, so that the arms are raised and lowered in accordance with the extension and retraction of the raising and lowering cylinders.
In such working vehicles, a construction in which an engine, a hydraulic pump and the like are disposed beneath the operating cabin, and the operating cabin is attached so that this operating cabin can be swung upward and downward in order to facilitate maintenance of the hydraulic pump and the like, is also generally known. In this case, the operating cabin is pivotably connected to the moving body via dampers or the like, so that the operating cabin can be easily swung upward and downward by the manual operation of the operator with the aid of the dampers. In order to perform maintenance on the hydraulic pump and the like, the arms are first swung into the lower position so that the bucket is placed on the surface of the ground. Then, the bucket is removed from the arms. Next, the arms are caused to move upward so that the reinforcing member connected between the arms is moved to the upper position, thus forming a space in which the operator can move in a position in front of the vehicle. Then, the operator swings the operating cabin upward so that the hydraulic pump and the like positioned beneath the operating cabin are exposed, and performs maintenance work on the hydraulic pump and the like.
When maintenance work is being performed in this way, it is necessary to hold the arms in a state in which the arms have been raised upward. Here, since the extension and retraction operation of the raising and lowering cylinders that raise and lower the arms is controlled by a switching valve installed in the hydraulic pressure circuit, the hydraulic circuit must be cut off by this switching valve so that the extension and retraction operation of the raising and lowering cylinders is stopped in order to hold the arms in the raised position. However, even if the extension and retraction operation of the raising and lowering cylinders is thus stopped and held by the switching valve, there is a danger that oil may leak from gaps around the outer circumference of the spool of the switching valve so that there is a gradual retraction of the raising and lowering cylinders. In most cases, therefore, an arm lowering motion restricting device which securely restricts the retraction of the raising and lowering cylinders by mechanical means is mounted on the working vehicle.
Such arm lowering motion restricting devices include devices which comprise an arm restricting member, a locking pin and a tension spring. Furthermore, one end of the arm restricting member is pivotably connected to one of the arms, and the arm restricting member extends between this arm and the raising and lowering cylinder so that the upper surface of the raising and lowering cylinder is covered, with the arm restricting member being free to swing upward and downward. The other end of the arm restricting member is placed in a state in which this end contacts the cylinder tube of the corresponding raising and lowering cylinder, so that the retraction of the raising and lowering cylinder is mechanically restricted. The locking pin is inserted (in a manner that allows free insertion or removal) into the tip end portions of a pair of protruding parts formed on the arm restricting member, which protrude downward beyond the lower surface part of the cylinder rod of the raising and lowering cylinder so that the left and right sides of the cylinder rod are covered in a state in which the tip end portion of the arm restricting member is caused to contact the tip end surface of the cylinder tube, thus restricting the swinging of the arm restricting member in the direction that causes the tip end portion of the arm restricting member to move away from the tip end surface of the cylinder tube. One end portion of the tension spring is attached to the tip end portion of the arm restricting member, and the other end portion of the tension spring is attached to the locking pin, which is inserted (in a manner that allows free insertion and removal) into a bracket that protrudes downward from the undersurface of the arm in a state in which the tip end portion of the arm restricting member is caused to contact the tip end surface of the cylinder tube, so that the arm restricting member is pulled upward with respect to the raising and lowering cylinder.
Here, in order to release the restriction of the retraction of the raising and lowering cylinder from the state in which the retraction of the raising and lowering cylinder is restricted by the contact of the tip end portion of the arm restricting member with the tip end surface of the cylinder tube, the locking pin that is inserted into the arm restricting member is pulled out, the other end portion of the tension spring is fastened to the locking pin, and the locking pin is inserted into the bracket in this state. Then, when the raising and lowering cylinder is extended so that the tip end portion of the arm restricting member is caused to separate from the tip end surface of the cylinder tube, the tension spring causes the arm restricting member to swing upward as a result of the tensile force of the spring, so that the tip end portion of the arm restricting member is removed from the tip end surface of the cylinder tube, thus releasing the restriction of the retraction of the raising and lowering cylinder.
Thus, in order to release the restriction of the retraction of the raising and lowering cylinder, the locking pin is removed from the arm restricting member, after which the tension spring is fastened to the locking pin, and the locking pin is inserted into the bracket. However, when the locking pin is inserted into the bracket, the tension spring is in an extended state. Accordingly, the locking pin must be inserted into the bracket against the tension of the tension spring, so that this work is bothersome.
The present invention was devised in light of such problems; it is an object of the present invention to provide an arm lowering motion restricting device in which the releasing operation that releases the restriction of the retraction of the raising cylinder by the arm restricting member is easy.
In the present invention, a working vehicle comprises a vehicle, an arm which is attached to the vehicle so as to be freely raised and lowered, and a raising and lowering cylinder which is attached between the vehicle and the arm to raise and lower the arm, in which the tip end of a cylinder rod constituting the raising and lowering cylinder is pivotably connected to the arm, and a cylinder tube constituting the raising and lowering cylinder is pivotably connected to the vehicle, so that the arm can be raised and lowered by extending and retracting the cylinder rod from and into the cylinder tube. The arm lowering motion restricting device comprises an arm restricting member one end of which is pivotably connected to the arm, and which extends between the arm and the raising and lowering cylinder so as to cover the upper surface of the raising and lowering cylinder, and is free to swing upward and downward about the position where the one end is pivotably connected to the arm; a swinging motion restricting member which restricts the swinging motion of the arm restricting member in the direction where the arm restricting member is separated from the cylinder rod in a state in which the arm restricting member has swung into a position where the arm restricting member covers the top of the cylinder rod; and a swinging motion urging member which is attached to the other end of the arm restricting member, and which urges the arm restricting member in the direction where the arm restricting member is separated from the cylinder rod in a state in which the arm restricting member has swung into a position where said arm restricting member covers the top of the cylinder rod.
In the arm lowering motion restricting device constructed as described above, the arm restricting member covers the cylinder rod in a state in which the amount of extension of the raising and lowering cylinder has reached a specified amount, and the abovementioned second end portion of the arm restricting member can restrict the retraction of the raising and lowering cylinder by contacting the tip end surface of the cylinder tube. In this case, the swinging motion restricting member maintains a state in which the arm restricting member covers the cylinder rod, so that the retraction of the cylinder rod can be securely restricted. Meanwhile, when this restriction is to be released, if the restriction by the swinging motion restricting member is released, and the raising and lowering cylinder is slightly extended, the urging force of the swinging motion urging member causes the arm restricting member to swing in the direction that separates the arm restricting member from the cylinder rod, so that the restriction is automatically released. Accordingly, the work of releasing the restriction effected by the arm restricting member is simple.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.